Question

I have a problem with implementing touch events on GLSurfaceView. Views size is 1280×696, because of android (tablet) status bar at bottom with soft keys, time etc.., (screen resolution is 1280×800), but OnTouchListener is receiving touch events with coords [646.0,739.0], and thus my gluunproject method fails to return correct values
is there any way to return events that respect these boundaries? or how should I recalculate the position?

Answer 1

In general to transition between such coordinate systems: If you transition from system A to B and you have points

• AOrigin (left upper corner of your receiver view)
• AEnd (right bottom corner of your receiver view (origin + size))
• BOrigin (left upper corner of your GL view)
• BEnd (right bottom corner of your GL view (origin + size))

where AOrigin and BOrigin represent the same location in view and same goes for AEnd and BEnd
then for point P in the receiver view:

X = B.Origin.x + ((P.x - AOrigin.x)/(AEnd.x - AOrigin.x)) * (BEnd.x - B.Origin.x)
Y = B.Origin.y + ((P.y - AOrigin.y)/(AEnd.y - AOrigin.y)) * (BEnd.y - B.Origin.y)

For your case (I’m not sure because of lack of information) AOrigin is at (0,0), AEnd is at (646, 739), BOrigin is at (0,0) and BEnd is at (1280, 800):

X = P.x/646 * 1280
Y = P.y/739 * 800

You can also use this to transition to/from “GL” coordinates. A common case is having a view with upper left corner at (0, 0) and lower bottom at (1280, 800) and your “GL” coordinates are from (-1, 1) to (1, -1):

X = -1 + (P.x/1280)*2
Y = 1 + (P.y/800)*(-2)

Also note that you may use any 2 pairs of points that represent same location on screen as long as (origin-end).x != 0 AND (origin-end).y != 0